Garment-Integrated Silver-Based Interdigitated Capacitive Pressure Sensor Fabricated by Microdispensing for Elbow Motion Detection

Abstract

Garment-integrated wearable sensor devices are becoming essential for daily motion monitoring. The direct ink writing (DIW) technique offers a promising solution by enabling direct printing onto flexible substrates that can be seamlessly integrated into garments. Unlike conventional printing methods that require multiple layers or masking steps, the proposed approach enables rapid, precise dispensing through controlled deposition of conductive inks onto the substrate. This letter presents a thermoplastic polyurethane (TPU)-based silver (Ag) ink formulation for DIW fabrication of a flexible capacitive sensor, ensuring strong interfacial bonding with the TPU substrate and enabling seamless integration into garments. The developed sensor demonstrated stable and reproducible capacitance responses under repeated mechanical loads, achieving a sensitivity of 0.343 $\mathrm{kPa^{-1}}$ and pressure sensing up to 20 kPa and a high durability of 5500 loading/unloading cycles. As a proof of concept, the sensor was heat-transferred onto a textile sleeve for elbow motion detection. It functioned as a pressure sensor by detecting touch through capacitance changes. Tests in two wearable scenarios with five separate attempts, with 20 repetitions each showed consistent, reliable performance (p = 0.357 > 0.05).